Reg Dunlop, a University of Canterbury mechanical engineer who
specialised in robotics, responded.

The ant is stronger. I don't know much about ants but I'd love to be able to
make a "roboant" with the same size and strength as an ant.

While a human can pick up and carry a heavier weight for a greater distance
than an ant, the ant can carry much more in terms of its body weight,
and for longer distances in terms of its body length.

Often small sized creatures are stronger in terms of being able to carry
items that weigh more than they do. The load carrying capacity of bones
depends on the area through the bone (or external skeleton). Thus if the
creature is made twice as big, the length of the bone is also doubled (x2),
but the area becomes four times larger and the bone can carry four times
(2x2) as much weight. The body weight depends on the volume of the creature,
so if the size is doubled, the weight increases by eight times (2x2x2).

Thus if an ant was made twice as big, its "bones" would need to be eight
times larger in cross-sectional area i.e. almost three times thicker for it to
be as strong as before. If scaled up to human size, most of an ant's strength
would be used up just carrying around the bigger body, and the strength
would be similar to that of a human.

Here is something for you to think about. Why do moa and dinosaur have such
large heavy bones.